The 1983 Altos Model 5-15ED was an 8 bit microprocessor based system with dual floppy and Winchester hard disk together with single board microcomputer technology.

The Altos Series 5 computer system was a Z80A-based multiuser system designed to fit many commercial, technical, industrial, Scientific, and educational applications. It ran under either CP/M, MP/M II, or OASIS operating systems. In its basic figuration, the system was contained in a single chassis, however additional chassis could be connected to the basic chassis to increase system capabilities*

The basic computer system includes the CPU, four RS-232-C ports, one parallel port, 192 kilobytes of RAM, all peripheral Controllers, and one 5-1/4 inch floppy disk drive. You have to add a keyboard terminal, provide your own floppy diskettes and cabling.

Series 5-5D also included a five-megabyte drive and a five-inch hard disk drive.Series 5-15D also included a second one-megabyte disk drive unit.

CP/M (Control Program for Microcomputers), created by Gary Kildall in 1974 for Intel 8080-based systems, was the first widely adopted microcomputer operating system to establish a standard software platform. At its core, CP/M was divided into three layers: the BIOS (Basic Input/Output System) for hardware-dependent routines, the BDOS (Basic Disk Operating System) for file and device abstractions, and the CCP (Console Command Processor) for the command-line interface. This modular design meant CP/M could be ported to a wide variety of 8-bit systems simply by rewriting the BIOS layer, while the BDOS and CCP remained binary-compatible. This allowed application developers to target a single OS API rather than custom hardware interfaces, which was a radical departure from the fragmented landscape of early microcomputers.

Memory management in CP/M was constrained by the 8080 and Z80’s 64 KB address space, so the operating system was designed to occupy only the top portion of memory. The BDOS and CCP were typically loaded into high memory, leaving a contiguous block of low memory available for transient programs (user applications). Applications were written to expect a fixed TPA (Transient Program Area), with the starting address varying slightly depending on how much memory was available after BIOS/BDOS were loaded. This simple scheme avoided the need for virtual memory or sophisticated protection mechanisms, but it limited multitasking: CP/M was strictly a single-tasking environment. Program overlays and clever memory swapping techniques were sometimes used by developers to fit larger applications into the available TPA, especially for compilers and database software.

Application support was the main driver of CP/M’s dominance. Its standardization around the BDOS interface meant that word processors, assemblers, compilers (notably for C, Pascal, and BASIC), and business applications could run on hundreds of different hardware platforms with minimal modification. Programs were distributed as .COM files—binary images loaded directly into the TPA without relocation—which simplified the loader at the cost of flexibility. Libraries like Digital Research’s PL/I subset and third-party toolchains extended CP/M into a development platform, while the vast ecosystem of utilities (from editors like ED to debuggers and communications software) established it as the de facto operating system of the late 1970s and early 1980s microcomputing world. For retrocomputing enthusiasts, CP/M represents the moment when software compatibility, not just hardware, became the central value in the microcomputer marketplace.

MP/M (Multi-Programming Monitor Control Program), introduced by Digital Research in 1979, was a multitasking and multiuser extension of CP/M for Intel 8080 and Z80 systems. It retained the same modular structure of BIOS, BDOS, and CCP, but extended the BDOS to support task scheduling, memory partitioning, and multiple console I/O streams. Instead of a single Transient Program Area (TPA), MP/M divided available RAM into multiple partitions, each capable of running a separate process. A priority-driven scheduler controlled task execution, allowing background and foreground jobs, and a sophisticated interrupt handling system enabled multiple users to interact with the system simultaneously through connected terminals.

The key differences between MP/M and CP/M centered on concurrency and resource sharing. Where CP/M was strictly single-tasking with one console and one TPA, MP/M could handle multiple programs and users at once, with independent console sessions mapped to serial ports. It also introduced file locking and record management to prevent corruption when multiple processes accessed the same data, and supported spooling for printers and batch jobs. These enhancements required more RAM and CPU performance than CP/M, which limited MP/M’s adoption on low-end 8-bit systems. Nonetheless, MP/M laid the groundwork for Digital Research’s later Concurrent CP/M and CP/M-86 derivatives, bridging the gap between the simplicity of CP/M and the more complex, multiuser operating systems found on minicomputers.

OASIS (Operating System for Advanced Intelligent Systems) was a multiuser, multitasking operating system developed by Phase One Systems in the late 1970s for 8-bit microcomputers, particularly those based on the Zilog Z80. Unlike CP/M, which was designed as a single-tasking, single-user environment, OASIS was architected from the start to handle multiple concurrent users on a single machine, with terminal connections managed via serial interfaces. It implemented a hierarchical file system, device-independent I/O, and real-time task scheduling, bringing minicomputer-class functionality into the microcomputer world. Its memory management strategy partitioned RAM to maintain separate user contexts while providing system services in a protected kernel area, enabling true timesharing on hardware that was otherwise quite limited.

One of OASIS’s distinguishing features was its integrated environment: it shipped with a full suite of development tools (including a COBOL compiler, BASIC interpreter, and business-oriented utilities), as well as database and word processing applications. This turnkey approach made it attractive for small and medium-sized businesses seeking multiuser capability without investing in expensive minicomputers. Compared to CP/M or even MP/M, OASIS was more complete as a business system but was tied to its proprietary ecosystem, limiting third-party software availability. Despite its relative obscurity today, OASIS demonstrated that multiuser operating systems could be implemented effectively on 8-bit microcomputers, prefiguring the role that systems like Xenix and UNIX derivatives would later play on 16-bit platforms.

The Z80 quickly became popular in the personal computer market, with many early personal computers, such as the TRS-80 and Sinclair ZX80, using the Z80 as their central processing unit (CPU). It was also widely used in home computers, such as the MSX range, SORD, and the Amstrad CPC, as well as in many arcade games. Additionally, it was also used in other applications such as industrial control systems, and embedded systems. The Z80 was widely used until the mid-1980s, when it was gradually replaced by newer microprocessors such as the Intel 80286 and the Motorola 68000.

The Z80 microprocessor was developed by Zilog, a company founded by Federico Faggin in 1974. The Z80 was released in July 1976, as a successor to the Intel 8080. It was designed to be fully compatible with the 8080, but also included new features such as an improved instruction set, more powerful interrupts, and a more sophisticated memory management system.

Originally the Z80 was intended for use in embedded systems, just as the 8080 CPU. But the combination of compatibility, superior performance to other CPUs of the era, and the affordability led to a widespread use in arcade video game systems, and later in home computers such as the Osborne 1, TRS-80, ColecoVision, ZX Spectrum, MSX, Sega's Master System and many more. The Z-80 ran the original Pac-Man arcade cabinet. The Z-80 was used even in the Game Gear (1990s), and the TI-81 and succeeding graphic calculators.

The Z-80 remained in production until June of 2024, 48 years after its original release. Zilog replaced the processor with its successor the eZ80, an 8-bit microprocessor that features expanded memory addressing up to 16 megabytes, and running up to 50MHz, comparable to a Z80 clocked at 150MHz.